全文获取类型
收费全文 | 12384篇 |
免费 | 1140篇 |
国内免费 | 907篇 |
专业分类
电工技术 | 65篇 |
技术理论 | 1篇 |
综合类 | 550篇 |
化学工业 | 7858篇 |
金属工艺 | 605篇 |
机械仪表 | 156篇 |
建筑科学 | 177篇 |
矿业工程 | 181篇 |
能源动力 | 796篇 |
轻工业 | 343篇 |
水利工程 | 66篇 |
石油天然气 | 359篇 |
武器工业 | 1095篇 |
无线电 | 289篇 |
一般工业技术 | 1225篇 |
冶金工业 | 265篇 |
原子能技术 | 137篇 |
自动化技术 | 263篇 |
出版年
2024年 | 13篇 |
2023年 | 185篇 |
2022年 | 195篇 |
2021年 | 312篇 |
2020年 | 368篇 |
2019年 | 368篇 |
2018年 | 380篇 |
2017年 | 362篇 |
2016年 | 372篇 |
2015年 | 520篇 |
2014年 | 909篇 |
2013年 | 833篇 |
2012年 | 917篇 |
2011年 | 1146篇 |
2010年 | 927篇 |
2009年 | 969篇 |
2008年 | 794篇 |
2007年 | 797篇 |
2006年 | 686篇 |
2005年 | 627篇 |
2004年 | 479篇 |
2003年 | 499篇 |
2002年 | 301篇 |
2001年 | 240篇 |
2000年 | 235篇 |
1999年 | 200篇 |
1998年 | 130篇 |
1997年 | 93篇 |
1996年 | 101篇 |
1995年 | 76篇 |
1994年 | 62篇 |
1993年 | 56篇 |
1992年 | 87篇 |
1991年 | 40篇 |
1990年 | 35篇 |
1989年 | 34篇 |
1988年 | 10篇 |
1987年 | 17篇 |
1986年 | 15篇 |
1985年 | 8篇 |
1984年 | 9篇 |
1983年 | 5篇 |
1982年 | 6篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1976年 | 1篇 |
1974年 | 1篇 |
1960年 | 1篇 |
1959年 | 1篇 |
1951年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 438 毫秒
41.
42.
43.
Gong-Liang Li Ishihara Tatsumi Moro-oka Yoshihiko Takita Yusaku 《Applied catalysis. B, Environmental》1996,9(1-4):239-249
The catalytic decomposition of CHClF2 was studied over various acidic metal oxides in a fixed-bed reactor. The Cr2O3ZrO2 exhibited the highest activity. The presence of water vapor in the reaction system suppresses the transformation of oxides to fluorides, progresses the formation of CO2, and it improves the catalysts life. 相似文献
44.
S. Suppan J. Trawczyski J. Kaczmarczyk G. Djga-Mariadassou A. Hynaux C. Sayag 《Applied Catalysis A: General》2005,280(2):209-214
Carbon black composites (CBCs) have been prepared by pyrolyzing mixture of a carbon black with polyfurfuryl alcohol and then pretreated by oxidation with nitric acid, gasification with water steam or ammoxidation. The effects of the chemical character of the carrier surface, nature of the active metal phase and pH value of the impregnation solution on the catalytic activity towards the hydrodesulfurization (HDS) of thiophene of the CBC supported Mo (Co) catalysts were determined. It was stated that the catalytic properties of the CBC supported sulfides of Mo or Co and of Mo carbides are affected by the chemical character of the carrier surface. Generally, catalysts supported over basic surface CBC exhibit higher activity than those ones supported over CBC possessing acidic surface character. Co catalysts supported on acidic surface show lower activity (per mol of active metal) than Mo based ones supported on the same carrier. In the case of catalysts supported on basic CBC, Co exhibits distinctly higher activity than Mo. At the experimental conditions adopted for this study, CBC surface properties, active phase nature, and catalyst impregnation pH were found to exert a relatively small influence on both HDS and hydrogenation activities. 相似文献
45.
Selectivity of partial hydrogenation reactions performed in a pore-through-flow catalytic membrane reactor 总被引:2,自引:0,他引:2
The selectivity of partial hydrogenation reactions of unsaturated substrates was studied in a membrane reactor operating at 323 K and 40 bar hydrogen pressure. The reactor system was constructed as a loop of a saturation vessel and a membrane module in which the reaction mixture was resaturated with hydrogen up to 100 times. In a porous membrane made from cross-linked polyacrylic acid palladium nanoparticles were incorporated as catalysts. A well-defined residence time within the membrane was achieved due to a defined pore structure of the membrane and a convective mass flow of the reaction mixture through the membrane. The selectivity for the partially hydrogenated products was investigated as a function of the pore size of the PAA membrane and was compared to commercially available catalysts. Compared to experiments with supported catalysts (Pd/C and Pd/Al2O3) in a slurry and a fixed bed reactor the selectivity for the desired products could be increased by 3% (1-octyne) up to 40% (geraniol). 相似文献
46.
A new method for analysis of trace mercury in water samples was developed, based on the combination of preconcentration/separation using dithizone-modified nanometer titanium dioxide (TiO2) as a solid phase extractant and determination by cold vapor atomic adsorption spectrometry (CVAAS). Dithizone was dissolved with alcohol and loaded on the surface of nano-sized TiO2 powders by stirring. The static adsorption behavior of Hg2 on the dithizone-modified nanoparticles was investigated in detail. It was found that excellent adsorption ratio for Hg2 could be obtained in the pH range of 7-8 with an oscillation time of 15 min, and a 5 mL of 3.5 mol·L-1 HCl solution could quantitatively elute Hg2 from nanometer TiO2 powder. Common coexisting ions caused no obvious influence on the determination of mercury. The mechanisms for the adsorption and desorption were discussed. The detection limit (3σ) for Hg2 was calculated to be 5 ng·L-1. The proposed method was applied to the determination of Hg2 in a mineral water sample and a Zhujiang River water sample. By the standard addition method, the average recoveries were found to be 94.4%-108.3% with RSD (n = 5) of 2.9%-3.5%. 相似文献
47.
本文阐述了计算机软件在多媒体化学课件开发中的应用,着重介绍了一些普通软件及专业化学软件的特点及功能。 相似文献
48.
Exchanges of total N and C between a river and its floodplain forest have been enhanced by sedimentation processes during flood pulses at a 5‐ha bottomland hardwood forest located at the Olentangy River Wetland Research Park in central Ohio. In the spring of 2000, the forest was hydrologically restored by notching an artificial levee that had separated the Olentangy River and its floodplain forest for 100 years. One‐hundred flat sediment traps (30 cm × 30 cm) were used to collect sediment samples during spring/summer flooding events from 2003 to 2005. Results showed that sediment deposition is determined by the landscape variability during flooding events, Net sediment deposit in the wettest area averaged 134 ± 12 g‐dry wt m?2 in 2003, 127 ± 17 g‐dry wt m?2 in 2004 and 149 ± 23 g‐dry wt m?2 in 2005. Total N and C sedimentation ranged from 0.49 to 0.92 g‐N m?2 and 5.2 to 19.9 g‐C m?2. Fe dominates the sediment chemistry and results show the elemental abundance in the order of Al > Fe > Ca > K > Mg > S > P > Na > Mn > Zn > B > Cu > Mo. A hydrologic pulsing index (HPI) could be used as an indicator for mass changes of energies with hydrologic pulsing events. Restoration of seasonally flooded bottomland forests could stimulate potentially large nutrient and Fe releases, which would eventually lead to an enhanced forest productivity and biodiversity. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
49.
50.
文中介绍了工程化学基础课程改革思想的提出,在教改过程中通过遴选合适的教材、修订教学大纲,建全教学文件、适当运用现代化教学手段和积极进行师资队伍建设等改革方案的实施,在教学实践中适应科技发展,培养工程概念,增强环保和经济意识,及时更新教学内容,提高教学质量。 相似文献